Is it possible to set the opacity of qt widgets?

Question

I know that there is a function QWidget::setWindowOpacity(qreal level) but as written in the documentation this does only work for windows.

Is there a way to make widgets that are lying inside layouts opaque too?

What I'm trying to do is an animation where widgets are fading in. I once did that with a preferences-dialog and there it worked.

So do you think there is a way or a work-around to achieve opacity for widgets inside layouts? How would you do that?

Thanks in advance!

Parma

If you have no background under widget, maybe you can change widget color starting from background color. – La

There is a similar question Animate transparency.. with a code example. – Akkad

Answer 1

Just use QGraphicsOpacityEffect in order to achieve this effect.

• Qt4: http://doc.qt.io/qt-4.8/qgraphicsopacityeffect.html
• Qt5: http://doc.qt.io/qt-5/qgraphicsopacityeffect.html
• Qt6: https://doc.qt.io/qt-6/qgraphicsopacityeffect.html

Bethlehem

Answer 2

Well for widgets inside mainwidow appear to have setAutoFillBackground(False) by default.

to make it fade in fadeout u need to to use QGraphicsOpacityEffect along with setAutoFillBackground(True)

a small example: write inside the widget which is called inside the mainwindow

op=QGraphicsOpacityEffect(self)
op.setOpacity(1.00) #0 to 1 will cause the fade effect to kick in
self.setGraphicsEffect(op)
self.setAutoFillBackground(True)

Beefy

Setting setAutoFillBackground on a child of a central widget did the trick for me: opacity effect now works for the widget. Any idea why setting that is required? – Vally

Answer 3

SetWindowOpacity works for me in Linux. I used code like this to change window opacity, (value is from 0 to 100):

setWindowOpacity(qreal(value)/100);

Westcott

This works for windows, but not for widgets which are part of a layout etc. At least for me, I am using Microsoft Windows. – Parma

Ah, I misunderstanded. I though you mean MS Windows xD – Westcott

Answer 4

mywidget.setStyleSheet('background-color:rgba(r, g, b, alpha);') 

works for me

Trustworthy

Please look at formatting the code in your answer to make it easier to read. – Merkley

Answer 5

In Qt5 you can use css to make widgets transparent

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QDialog dialog;
    dialog.setStyleSheet(QLatin1String("#LolButton{color: transparent; background-color: transparent;}"));
    QPushButton button(&dialog);
    button.setText("Button");
    button.setObjectName(QStringLiteral("LolButton"));
    QObject::connect(&button,&QPushButton::clicked,[](){
        QMessageBox msg;
        msg.setText("LolButton omg");
        msg.exec();
    });
    dialog.show();
    return a.exec();
}

Salvador